Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase.
In some approaches, positive crankcase ventilation (PCV) systems may use steady state pressure differences to inject fresh air into the crankcase or pull fresh air mixed with blow-by gases out of the crankcase. For example, in some approaches a breather or vent tube may couple the crankcase to a fresh air intake upstream of the throttle and another PCV conduit may couple the crankcase to the intake manifold downstream of the throttle so that pressure differences between the fresh air intake and the intake manifold may be used to drive flow of PCV gases through the crankcase.
However, the inventors herein have recognized that in such approaches the direction of flow through the crankcase ventilation system may change depending on engine operating conditions. Such bidirectional flows through crankcase ventilation systems may increase costs associated controlling and monitoring the crankcase ventilation system and reduce effectiveness of gas evacuation from the crankcase thus potentially increasing emissions and crankcase degradation.
For example, in such approaches ventilation gases may flow in a direction through the crankcase from the fresh air intake to the intake manifold during a first condition and ventilation gases may flow in a direction from the intake manifold to the fresh air inlet during other conditions. In such approaches, since crankcase ventilation gases have a bidirectional flow, multiple oil separators may be employed which increases costs associated with the inclusion of oil separators and associated sensors or valves. For example, in such approaches an oil separator may be coupled to the breather tube and another oil separator may be coupled to the PCV conduit to substantially prevent oil from entering the engine intake.
Further, since in such approaches gas flow through the ventilation system depends on steady state pressure differences in the intake manifold, the gas flow through the crankcase ventilation system may be reduced during certain conditions which may be disadvantageous for boosted engines or engines which have high exhaust humidity, e.g., engines fueled with ethanol or methanol, which require increased crankcase ventilation. Further, in such approaches steady flow rates may be disrupted and fall below a threshold needed to keep oil separator efficiency high. For example, low crankcase pressure may be favorable for turbochargers with hydrodynamic bearings, e.g. journal bearings. Further still, since in such approaches the crankcase gasses combined with ventilation air bypass the throttle, the ability of the throttle to control to low air flow rates may be degraded.
Thus, in one approach, to at least partially address these issues, a method for an engine with a crankcase ventilation system is provided. The method comprises driving flow of crankcase ventilation gases through a crankcase of the engine from a fresh air inlet of the crankcase to an outlet of the crankcase via crankcase pressure pulsations while restricting backflow of crankcase ventilation gases from the outlet to the inlet, where the inlet and outlet are coupled upstream of an intake throttle of the engine.
In this way, crankcase pulsation energy may be used to drive crankcase ventilation flow and a check valve at the crankcase's fresh air inlet or mixed air outlet may rectify the flow pulsations to create a unidirectional flow. Such a unidirectional system has the potential advantage of requiring only one oil separator instead of two, resulting in a reduction in costs. Further, such an approach increases ventilation gas flow and control while reducing costs associated with sensors and valves for monitoring, oil separation and control. For example, low engine air flow rate control to the throttle may be increased since it is no longer bypassed to power PCV flow and flow rates in excess of a threshold amount may be used to provide a constant flow rate to an oil separator.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.